The present invention relates to a semiconductor device and a method of connecting the same.
Recently, a universal serial bus (USB) is used as an interface standard for connecting a personal computer to peripheral devices such as a keyboard and mouse. This USB can connect peripheral devices in the form of a tree via a hub, thereby connecting a maximum of 127 peripheral devices by one port.
The USB also has a so-called hot plug function by which cables can be connected and disconnected with the power supply being kept on.
Devices connected to this USB can be classified into a host such as a personal computer which controls the whole system, a hub which relays data transfer, and devices as peripheral equipment which operate under the control of the host.
In addition, the USB has four signal lines, i.e., a power line VBUS which supplies a power supply voltage of, e.g., 5 V, a ground line GND for grounding, a data plus line DP, and a data minus line DM, and performs differential signal transmission by using the data plus line DP and data minus line DM.
The USB defines a full speed of 12 Mbits/sec and a low speed of 1.5 Mbits/sec as the data transfer speeds of devices. Therefore, the USB is connected to both devices (e.g., a printer and hard disk drive) which operate at a full speed of 12 Mbits/sec, and devices (e.g., a mouse and keyboard) which operate at a low speed of 1.5 Mbits/sec. The host or hub performs data transfer corresponding to the data transfer speed of a connected device.
Accordingly, the host/hub must identify whether the connected device is a device which operates at the full speed or a device which operates at the low speed.
When a device is connected, the host/hub checks whether the data transfer speed of the connected device is the full speed or low speed, on the basis of the potentials of the data plus line DP and data minus line DM. However, the data transfer speed is sometimes incorrectly judged owing to noise generated on the data plus line DP and data minus line DM.